Apparatus for electrochemical fluid analysis



March 3, 1959 s. B. SPRACKLEN ET AL 2,876,189

APPARATUS FOR ELECTROCHEMICAL FLUID ANALYSIS Filed Feb. 15, 1956 L L g? 1% Sample \f Gas -20 Ve+nf Vehf 4 l I I0 15 t I r J, 3/? J 4', v A l'f in 7 g n d r g Recording lnsfrumenf Glass Beadsv 2. INVENTORS ATTORN Y STANFORD B. SPRACKLEN United States Patent" APPARATUS FOR ELECTROCHEMICAL FLUID ANALYSIS Stanford B. Spracklen, Hurricane, Donald N. Campbell, St. Albans, and Charles G. Fellows, Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York Application February 13, 1956, Serial No. 564,942

6 Claims. (Cl. 204-195) The present invention relates to a method and apparatus for the continuous measurement of one constituent in a stream of process fluid, referred to hereinafter as the sample flui 1 In the continuous analysis of constituents of a fluid mixture with an instrument having a full scale range of 100 parts per million, the problem of sorting out-and in some way tagging and countingso few parts in so many becomes extremely difficult.

Heretofore, a method of analyzing sample fluids for detecting and quantitatively measuring for one constituent of a fluid mixture in the parts per million range has been proposed employing what may be referred to as the con centration cell principle. A concentration cell is one in which two bodies of electrolyte, one having an ionic content different from the other in magnitude and/or kind, are placed together so that a liquid interface obtains and an ionic gradient exists across this interface which causes an electrical potential to occur between two electrodes of the same material, one of which is contacted with each body of electrolyte. Most prior apparatus based on the concentration cell principle employed heretofore was not applicable to the continuous measurement for one constituent of a flowing sample fluid stream due to the difficulties encountered in maintaining a definite interface -between the two electrolyte components of the cell. In those few prior apparatus proposed for continuous measurement, the requirement of maintaining'a definite interface between the two electrolyte components of the cell was so critical that diffusion barriers, such as salt bridges, diaphragms, or the like, were required to properly separate the two electrolyte components. This resulted in low speed response and complicated apparatus.

Another prior method was proposed employing photochemical means for quantitatively measuring for one constituent of a sample fluid mixture. This method is disclosed andclaimed in U. S. Patent application Serial No. 374,941 filed August 17, 1953 by S. B. Spracklen and C. G. 'Fellows and now abandoned. As disclosed therein, a method is provided for continuously analyzing for parts per million of oxygen in a sample fluid by measuringthe relative change in turbidity effected in a reagent solution by chemical reaction with the oxygen contained in the sample gas. Although such method provided a continuous measurement of oxygen content in theparts per million range, it presented the difliculty of having an inherently slow response time. The measurement'principle there involved required, for effective measurement, a high ratio of sample fluid flow to reagent solution flow which, in turn, necessitated a large liquid hold-up time and resulted in a slow speed of response of the analyzer. Accordingly, if rapid changes in oxygen gas content were effected in the sample fluid, an indication of such changes could not be made for a considerable time period after the change. This means that such a method andapparatus was limited in utility to use with systems in which only slow uniform changes or drifts occurred, and was not i capable of use with systems which provided large, rapid "ice - Other aims and advantages of the invention will be ap-v parent from the following description and appended claims. 7

In accordance with the method of the present invention, a stream of suitable reagent electrolyte solution is continuously contacted with a flowing stream of sample fluid mixture containing the constituent to be measured for, and this constituent operates to etfect a change in the ionic content of the reagent electrolyte solution. The treated reagent electrolyte solution stream is then passed in contact with one of a pair of parallel, spaced electrodes, while another stream of untreated reagent electrolyte solution is concurrently passed in contact with the other of the electrodes so as to form and maintain an interface between the twoflowing streams of electrolyte solution. In this manner, what may be termed a dynamic concentration cell is provided which results in the development' across the electrodes of a potential which is proportional to the concentration in the sample fluid mixture of the constituent to be measured for. The electrodes employed should be composed of a material that does not react with the reagent electrolyte solution employed, nor with the constituent of the sample fluid mixture to be measured. Unless the electrode materials are inert to this extent, corrosion or other chemical reactions will result in erratic operation and a faulty measurement. I

The-reagent electrolyte solution employed must be selected in terms of the constituents of the sample fluid mixture and so as to be effected in ionic content only by the constituent to be measured for and not by the other constituents of the sample fluid mixture. For example, a solution of ammoniacal ammonium chloride containing cuprous ammonium ions may be employed as the reagent for quantitatively measuring the oxygen gas content of a sample fluid mixture not having other constituents capable of chemically reacting with that solution or capable of oxidizing the cuprous ammonium ions to cupric ions.

The hydrogen chloride content of a gas mixture can be removed from the mixture by scrubbing in water and the ionic difference between the water before and after scrubbing can be calibrated as the hydrogen chloride concentration of the sample gas mixture, provided that the sample gas mixture does not contain other ionizable constituents.

Carbon dioxide and other gases may be scrubbed from a gas mixture by employing a suitable scrubbing solution and a concentration measurement can be effected in accordance with the method of the invention. The method is, therefore, operable for a wide variety of concentration measurements.

Apparatus suitable for performing the method of the invention is shown in the drawing wherein the single figure is a combined sectional view of the measuring cell block and a schematic flow diagram of the entire apparatus.

The operation of the embodiment of the drawing will be described hereinbelow with respect to the analysis of a sample gas mixture for oxygen concentration in the parts per million range As there shown, two inert electrodes 1 and 2, of carbon or other suitable material, are arranged in cell block 3 which is composed of an inert material such as plastic. The oxygen-containing sample gas enters the cell block through inlet conduit 4, as does the untreated reagent electrolyte solution which comprises a solution of ammoniacal ammonium chloride containing cuprous ammoproportional to the concentration of oxygen in the gas.

streamgand to the solution and sample gas flow rate ratio.- The asstreated reagent. electrolyte solution, then.

passes through passage 7, passage 8, containing packing 9 such as glass beads, and then through perforated or pervious electrode 1 to form one electrolyte of the concentration. cell. The gaseous constituents ofthe sample gas stream, other than oxygen, are carried from passage 5 through scrubber outlet vent 10.

Another stream of untreated reagent electrolyte solution. is introduced into the cell block Sthrough conduit 11 and passes between electrodes 1 and 2, in contact with electrode. 2 and the stream of treated reagent electrolyte passing. from and'past electrode 1, thereby forming a liquid interface and completing a dynamic concentration cellibctween electrodes 1 and 2. After passing through thespa'ce 12 between electrodesl and 2, the streams of treated and untreated reagent solution intermix in passage 13 and are carried from the cell block 3 through exit conduitl4 and line 17. Vent 15 provides means for passing, frompassagesS and 13, any of. the sample gas not vented-from the systemthrough scrubber, vent10.

Thus, a potential is continuously developed by the dynamic concentration cellmaintained between the electrodes-1 and 2 and is proportional to the oxygen concentration of the sample gas removed by the reagent electrolyte solution in scrubber section 5. This potential ismeasured between electrode contacts 16 which are connected either directly, or if desired, through amplifying means, to an indicating or recording instrument 25 which is calibrated to read in parts per million oxygen concentration,

For, ease of fabrication, thelarge-passages of the cell block are all of the same diameter andpassage 8 is filled with a packing material, such as glass beads, simply to reduce the volume of treated reagent electrolyte solution employed, thereby increasing the speed of response to a change in the measuring reagent electrolyte solution.

The mixture of. treated and untreated reagent electrolyte solution passed from the cell block 3 through conduit; ld and line 17 may flow into a reservoir 18 contain ing metallic copper 19 in the form of turnings of small pieces. of scrap, which, upon. contacting the cupric ions of. theptreated solution, causes them to be reduced to cuprous ions. In this manner, the entire solution is.re' stored: to the untreated condition (containing only cuprous 7 ions) whichmaythen be returned by pump 26=through lines 20 and 21. to inlet conduits 4 and 11, respectively, thereby, permitting continuous oxygen gas analysis emplaying a closed reagent solution system. Flow control valves 22, 23 and 24 are respectively provided in the lines 20'and 21 as well as in the sample gas inlet line 27. Ammonia lost in=the-system may be replenished by con tinuous additions-from an external supply (not shown) too-the; reservoirs or some'other point in the closed liquid cycle.

The apparatus of theembodiment of. the drawing'may be:.employed for the continuous'measurement of: oneconstituent. ofv awide varietyof sample: fluids by merely changing the selection of reagent electrolyte; solution, the apparatus: has construction: materials such. as plasma. glass,.,and.carbon which are: inert: to most solutime both organic and inorganic.

: Whatis claimed-is: l

,7 1-.; for continuously measuring, the concert-- tration of a selected constituent in a sample fluid mixture stream which comprises, cell block meanshaving a packed scrubber section for contacting streams of reagent electrolyte solution and said sample fluid mixture to effect a change in ionic content of said reagent electrolyte solution proportional to the concentration of said selected constituent, in the sample fluid mixture; conduit means for venting from said scrubber section the gaseous constituents of said sample fluid stream other than said.

selected constituent; a pair of solid electrodes having opposed surfaces in spaced, substantially parallel, relationship being of such composition that they reactwith neither the electrolyte nor the sample fluid; conduit means for passing said stream of a's-treat'ed reagent electrolyte solution fromsaid scrubber section through and in contact with one of said electrodes, said electrode being porous; conduit means. for passing a stream of untreated reagent electrolyte solution between said electrodes and in contact with the other of said electrodes so as to form a liquid interface between said streams and provide a dynamic concentration cell; and electric cit cuit indicating means, connected to said electrodes, rcsponsive to the potential developed across said electrodes, and calibrated to indicate the change in concentrationof said selected constituent of said sample fluid.

2. Apparatus for continuously measuring the concentration of a selected constituent in a sample fluid mixture stream which comprises, cell block means having a packed scrubber section for contacting streams of reagent'electrolyte solution and said sample fluid mixture to effect a change in ionic content of said reagent electrolyte. solution proportional to the concentration of said selected constituent in the samplefluid mixture; conduit means:

forv venting from said scrubber section the gaseous constituents of said sample fluid stream other than said selected constituent; a 'pair of solid electrodes having opposed surfaces in spaced, substantially parallel, relationship being of such composition that they react with.

trodes and in contact with the other of said electrodes:

so as to form a liquid interface between said streamsand provide a dynamic concentration cell; electric circuit indicating means, connected to said electrodes, responsive to the potential developed across said electrodes, and

calibrated to indicate the change in concentration of said selected constituent of said sample fluid; means for effecting regeneration of said treated reagent electrolyte'solution; and conduit means for recycling said regenerated reagent electrolyte solution to said cell blo'ckme'ans;

3; In an apparatus for continuously measuring the concentration ofa selected constituent of a sample fluid employing a concentration cell and means for reacting one portion of. the electrolyte utilized in said cell with the sample fluid to achieve an ionic unbalance in that portion of the electrolyte which is proportional to said concentration, the improvement comprising two solid electrodes positioned within cavity means havingopposed surfaces in spaced, substantially parallel, relationship, the first of said electrodes being porousfor passing a continuous flow of treated electrolyte through said electrode and across the exposed face thereof; second inlet means opening adjacent to said second electrodefor passing a continuous flow of untreated electrolyte in contact with the exposed face offsa'id second electrode; third conduit means communicating with said cavity means for removingureacted and unreacted electrolyte from said, cavity, thepositioningrof said conduitmeans and the fluidflow resulting v in" a dynamic/liquid interface between said reacted-and saidunreacted electrolytes. whereby an opera tive concentration cellv and apotential ditterence is; de-

veloped between said electrodes which is proportional to the ionic unbalance between the two electrolytes.

4. Apparatus for measuring a sample fluid which comprises, means for contacting streams of reagent electrolyte solution and said sample fluid to effect a change in ionic content of said reagent electrolyte solution; a pair of electrodes having opposed surfaces in spaced, substantially parallel, relationship and of such composition that they react with neither the electrolyte nor the sample fluid; conduit means for passing said stream of as-treated reagent electrolyte solution from said contacting means through and in contact with one of said electrodes, said electrode being porous; conduit means for passing a stream of untreated reagent electrolyte solution between said electrodes and in contact with the other of said electrodes so as to form a liquid interface between said streams and provide a dynamic concentration cell; and electric circuit indicating means connected to said electrodes, responsive to the potential developed across said electrodes.

5. Apparatus for continuously measuring the concentration of a selected constituent in a sample fluid mixture which comprises, means for contacting a stream of reagent electrolyte solution and said sample fluid mixture to effect a change in ionic content of said reagent electrolyte solution proportional to the concentration of said selected constituent in the sample fluid mixture; a pair of electrodes having opposed surfaces in spaced, substantially parallel, relationship and of such composition that they react with neither the electrolyte nor the sample fluid; conduit means for passing said stream of as-treated reagent electrolyte solution from said contacting means through and in contact with one of said electrodes, said electrode being porous; conduit means for passing a stream of reagent electrolyte solution between said electrodes and in contact with the other of said electrodes so as to form a liquid interface between said streams and provide a dynamic concentration cell; and electric circuit indicating means connected to said electrodes, responsive to the potential developed across said electrodes,

and calibrated to indicate the change in concentration of said selected constituent of said sample fluid.

6. Apparatus for continuously measuring the concentration of a selected constituent in a sample fluid mixture which comprises, means for contacting a stream of reagent electrolyte solution and said sample fluid mixture to effect a change in ionic content of said reagent electrolyte solution proportional to the concentration of said selected constituent in the sample fluid mixture; a pair of electrodes having opposed surfaces in spaced, substantially parallel, relationship and of such composition that they react with neither the electrolyte nor the sample fluid; conduit means for passing a stream of untreated reagent electrolyte solution through and in contact with one of said electrodes, said electrode being porous; conduit means for passing said stream of as-treated reagent electrolyte solution from said contacting means between said electrodes and in contact with the other of said electrodes so as to form a liquid interface between said streams and provide a dynamic concentration cell; and electric circuit indicating means connected to said electrodes, responsive to the potential developed across said electrodes, and calibrated to indicate the change in concentration of said selected constituent of said sample fluid.

References Cited in the file of this patent UNITED STATES PATENTS 1,970,342 Schlumberger Aug. 14, 1934 2,278,248 Darrah Mar. 31, 1942 2,289,610 Wallace July 14, 1942 2,382,381 Calvert et a1. Aug. 14, 1945 2,517,382 Brinker et a1. Aug. 1, 1950 FOREIGN PATENTS 768,577 France May 22, 1934 OTHER REFERENCES Article by MacHattie et 211., Industrial Engineering Chemistry (Analytical ed.), vol. 9, August 15, 1937, pp. 364-366. 

1. APPARATUS FOR CONTINUOUSLY MEASURING THE CONCENTRATION OF A SELECTED CONSTITUENT IN A SAMPLE FLUID MIXTURE STREAM WHICH COMPRISES, CELLS BLOCK MEANS HAVING A PACKED SCRUBBER SECTION FOR CONTACTING STREAMS OF REAGENT ELECTROLYTE SOULATION AND SAID SAMPLE FLUID MIXTURE TO EFFECT A CHANGE IN IRONIC CONNTACT OF SAID REAGENT ELECTROLYTE SOLUTION PROPORTIONAL TO THE CONCENTRATION OF SAID SELECTED CONSTITUENT IN THE SAMPLE FLUID MIXTURE; CONDUIT MEANS FOR VENTING FROM SAID SCRUBBER SECTION GASEOUS CONSITUENTS OF SAID SAMPLE FLUID STREAM OTHER THAN SAID SELECTED CONSTITUENT; A PAIR OF SOLID ELECTRODE HAVING OPPOSED SURFACE IN SPACED, SUBSTANTIALLY PARALLEL, RELATIONSHIP BEING OF SUCH COMPOSITION THAT THEY REACT WITH NEITHER THE ELECTROLYTE NOR THE SAMPLE FLUID; CONDUIT MEANS FOR PASSING SAID STREAM OF AS-TREATED REAGENT ELECTROLYTE SOULATION FROM SAID SCRUBBER SECTION THROUGH AND IN CONTACT WITH ONE OF SAID ELECTRODES, SIAD ELECTRODE BEING POROUS; CONDUIT MEANS FOR PASSING A STREAM OF UNTREARED REAGENT ELECTROLYTE SOULATION BETWEEN SAID ELECTRODES AND IN CONTACT WITH THE OTHER OF SAID ELECTRODE SO AS TO FORM A LIQUID INTERFACED BETWEEN SAID ELECTRODES PROVIDED A DYNAMIC CONCENTRATION CELL; AND ELECTRIC CIRCUIT INDICATING MEANS, CONNECTED TO SAID ELECTRODES, RESPONSIVE TO THE POTENTIAL DEVELOPMENT ACROSS SAID ELECTRODES, AND CALIBRATED TO INDICATE THE CHANGE IN CONCENTRATION OF SAID SELECTED CONSTITUENT OF SAID SAMPLE FLUID. 